Optical instrument for smoke determination



Jan. 19, 1960 W. 'P. YANT ET AL OPTICAL INSTRUMENT FOR SMOKEDETERMINATION Filed March 25, 1954 205527 C- you-05.406 BY JOHN RSTEANGL.

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United States Patent OPTICAL INSTRUMENT FOR SMOKE DETERMINATION WilliamP. Yant, Murrysville, Robert C. Hollohaugh,

Verona, and John P. Strange, Murrysville, Pa., assignon to Mine SafetyAppliances Company, Pittsburgh, 8., a corporation of PennsylvaniaApplication March 25, 1954, Serial No. 418,542 7 Claims. (CI. 88-14)fe'reiit smoke density. This system of density determination gives onlya rough estimate, because the results are subject to many influencesaffecting the reproducibility of the determinations. Variations inlighting and background, against which the smoke is viewed, must betaken into account. Different readings may be obtained on dull days andbright days and when the position of the observer is shifted. Readingsalso are influ'enced by variations in the illumination of the chart,which in all cases is illuminated by the ambient light that may bedifferent from that at the stack. Also, the observer must refocus hiseyes in shifting from the smoke to the chart. In an attempt to improveresults, smoke has also been viewed through a section of clear glassbetween darkened sections which represent standard densities. This stilldoes not eliminate errors due to variations in ambient light and to therequirement that the observer must refocus his eyes in looking from thesmoke to the density reference.

It is among the objects of this invention to provide an instrument,through which smoke can be observed and compared with a referencestandard that receives light from the same source as the smoke and thatappears to be located at about the same distance from the observer asthe smoke. V

In accordance with this invention the instrument is provided with areflecting plate, through only the central area of which the distantsmoke can be seen. Located in the instrument near the reflecting plateis a translucent reference disc that receives light rays from thevicinity of the smoke. Means are provided in the path of those raysafter they leave the disc for directing them in substantially parallelrelation against the reflecting plate around its clear central area. Theresult is that a reflection of the disc appears on the plate but itappears to be about the same distance from the observer as the smoke, soit is unnecessary to refocus the eye while malt-- ing a comparison. Theimage of the reference disc surrounds the smoke seen through the clearcentral area of the reflecting plate. The reference disc is divided intoareas of different light densities for visual comparison with the smoke.This instrument limits the field of vision to the area of the stack andeliminates stray light and the effect of ambient light.

The invention is illustrated in the accompanying drawings, in which-Fig. l is a perspective view of our instrument aimed at smoke issuingfrom a stack;

2,921,497 Patented Jan. 19, 1960 Fig. 2 is an enlarged longitudinalsection through the instrument;

Fig. 3 is a transverse section taken on the line III- III of Fig. 2; and

Figs. 4 and 5 are longitudinal sections, similar to Fig. 2, of two otherembodiments of the invention.

Referring to the first three figures of the drawings, a pair of parallelcylindrical barrels 1 and 2 are spaced apart a short distance by meansof a tube 3 connecting the barrels near their rear ends. The sides ofthe barrels at the opposite ends of the tube are provided with openings, so that both barrels open into the connecting tube. When theinstrument is used, it can be held with one of the barrels-in anyposition relative to the other, but for convenience of descriptionherein one barrel is shown above the other.

The upper barrel shown in the drawing is the sighting barrel, throughwhich smoke 4 issuing from a stack 5 is seen. The rear or ocular end ofthis barrel is provided with a sight opening 7, and the opposite end isprovided with a restricted light opening 8. In the back part of thesighting barrel, there is a reflecting plate 9 that extends atapproximately a 45 angle across the barrel. The plate, preferably glass,extends from the front edge of the side opening in the barrel upward andbackward so that it overlies the upper end of tube 3. The plate isdesigned for reflecting an image of a reference disc to the observer.For this purpose it is necessary that little or no light pass backwardlythrough the plate except through its clear central area through whichthe smoke is observed. Light can be prevented from striking the platearound the clear central area by providing it with a silver backing, inwhich case the central area is left unsilvered or is provided with ahole. However, it is preferred to mount a diaphragm 11 in the barrel ashort distance in front of the plate, to help keep stray light fromreaching the glass. The diaphragm has a small opening 12 in its center,through which the smoke can be seen. With such a diaphragm the imageplate can be clear glass, because the diaphragm will form a darkbackground that will cause the plate to act like a mirror.

The rear end of the lower barrel is closed, but its front end has alarge opening in it. Inside this barrel a reference disc 13 is mountedbetween a pair of transparent glass discs 14. This disc is made oftranslucent material and is divided into shaded areas, a, b, c, and d(Fig. 3) of different light densities comparing with the shaded areas ofa Ringelmann chart. In other words, each of the dif* ferent areas of thedisc is a different shade of gray. Only three or four of such areas arenecessary, and they meet at the center of the disc. The disc willreceive its light from the same source as the smoke because the lowerbarrel is aimed at the background area adjacent to the stack while thesmoke is being observed. The light rays passing through the referencedisc then strike a mirror 15 in the rear end of the lower barrel beneaththe connecting tube 3. This mirror is parallel to image plate 9 above itand therefore reflects the rays from the disc upward through the tubetoward the plate.

A major feature of this invention is that a lens 17 with a flat bottomand a convex top is mounted in the connecting tube of the instrument forthe purpose of bending the rays reflected from the mirror below it inorder to cause them to travel in parallel paths above the lens. The rayscome from the reference disc, which is located at the focal point of thelens. Since the rays from the reference disc therefore are parallel whenthey reach the eye of the observer, the reflection of the disc on theplate is an image that is projected to the stack being observed. Thedensity of the reference standards is chosen to provide a reflection onthe reflecting plate that is areas of a Ringelmann chart.

To prevent the central part of the reference disc from appearing on thereflecting plate and thereby being superimposed on the smoke seenthrough the plate, provision is made for blocking out the light raysfrom the central part of the disc when the reflecting plate does nothave a hole through its center. This blocking or occluding can be doneby a small circular disc 18 attached to the center of the lens or thecenter of the mirror 15 or even to the center of the reference discitself. Consequently, no reflection of the disc will reach the clearcenter of the reflecting plate, with the result that the reference discwill appear to surround the smoke seen through the plate. Comparison ofthe smoke density with the reference then can be made easily withoutchanging the focus of the eyes, because the reference will appear tosurround the smoke.

Another important advantage of the lens 17 is that it increases theintensity of the light coming from the refer ence disc. When the lightrays are reflected from the mirror, their intensity is reducedconsiderably, and although the disc receives more light through thelower barrel than the image plate receives through the upper barrel, thereflection of the disc on the plate might not be bright enough foreffective use. However, due to the lens, the light from the referencedisc which has been reduced by the mirror is increased again so that thereflection of the disc on the reflecting plate has the necessarybrightness and clarity.

Since the reference disc is not illuminated by ambient light at theobserver, but by the light from an area adjacent the smoke beingobserved, errors due to changes in ambient light are eliminated. Directcomparisons of smoke density and a reference standard can be made. Thelens 17 projects a virtual image of the reference to the stack,therefore making it unnecessary to refocus the eye in looking from thesmoke to the reference. Altogether, this instrument makes it possible tomake more accurate and consistent smoke density observations than havebeen possible in the past. 1

In the modification shown in Fig. 4, the sighting barrel 21 and itscontents are essentially the same as just described. On the other hand,the lower barrel 22 does not contain anything. It is connected to anopening in the front of a long vertical connecting tube 23. Behind thelower barrel the tube contains a mirror 24 for reflecting light rays upthrough the tube to the reflecting plate 25 in the upper barrel. Thereference disc 26 is mounted in the connecting tube below the lens 27,so light rays do not pass through the disc until after they have beenreflected by the mirror.

The instrument in Fig. has only one barrel 30 and that is vertical. Thetop is closed and the bottom open. Mounted at a 45 angle in the upperpart of the barrel is a reflecting plate 31 that has a silvered backaround a clear central area. An ocular opening 32 is formed in one sideof the barrel facing the mirror, while an objective opening 33 isprovided in the opposite side of the barrel. Directly below thereflecting plate there is a lens 35, and below that the reference disc36 is mounted. The lower end of the barrel has a large opening 37 belowobjective opening 33, and behind the large opening, a mirror 38 islocated for reflecting light rays up to the reflecting plate. Ifdesired, a light diffusion screen 39 may be mounted in the barreldirectly above the mirror.

According to the provisions of the patent statutes, we have explainedthe principle of our invention and have illustrated and described whatwe now consider to represent its best embodiment. However, we desire tohave it understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically illustratedand described.

We claim:

1. An optical instrument for the observation of smoke from a stack,comprising a rearwardly reflecting equivalent to the shaded platethrough only a central area of which the smoke can be seen by anobserver behind the plate, a translucent reference disc near the plate,means for directing light rays from only the vicinity of said smokethrough the disc while the smoke is being observed through said centralarea of the plate, and means in the path of said rays after they leavethe disc for directing them in substantially parallel relation againstthe rear face of the reflecting plate around said central area, saiddisc being divided into areas of different light densities for visualcomparison with the smoke.

2. An optical instrument for the observation of smoke issuing from astack, comprising a sighting barrel having an opening for light at itsfront end and an ocular opening at its rear end to permit said smoke tobe seen through the barrel, a rearwardly reflecting plate mounted in thebarrel at approximately 45 to its axis, means forming a dark backgroundfor all of the reflecting plate except a small central area throughwhichthe smoke can be seen, the side of the barrel opposite to the rearface of said plate being provided with an opening, a second barrelsubstantially parallel to the sighting barrel and having an opening inits front end, a mirror behind said last-mentioned opening and parallelto the reflecting plate for reflecting laterally light rays entering thesecond barrel through its front opening, a tube rigidly connected at oneend to the sighting barrel around its side opening, 'the tube beingpositioned to receive rays reflected from the mirror, a leans in saidtube in the path of said rays for directing them in substantiallyparallel relation against the rear face of the reflecting plate, atranslucent reference disc mounted in the instrument between the lensand said front end opening in the second barrel at about the focal pointof the lens, whereby the reflection of said disc on the reflecting platewill appear to be in space at a distance from the observer and tosurround the smoke seen through the reflecting plate, said disc beingdivided into areas of different light densities for visual comparisonwith the smoke, and means for keeping the central area of the disc frombeing seen on the reflecting plate.

3. An optical instrument as defined in claim 2, in which said referencedisc is mounted in said second barrel in front of the mirror.

4. An optical instrument as defined in claim 2, in which saidbackground-forming means is a diaphragm in the sighting barrel in frontof the reflecting plate.

5. An optical instrument for the observation of smoke issuing from astack, comprising a sighting barrel having an opening for light at itsfront end and an ocular open ing at its rear end to permit said smoke tobe seen through the barrel, a rearwardly reflecting plate mounted in thebarrel at approximately 45 to its axis, means forming a dark backgroundfor all of the reflecting plate except a small central area throughwhich the smoke can be seen, the side of the barrel opposite to the rearface of said plate being provided with an opening, a second barrelsubstantially parallel to the sighting barrel and provided in its sidewith an opening opposite to the side opening in the sighting barrel, ashort tube rigidly con- 50 necting said side openings, a mirror in thesecond barrel at the end of said tube and parallel to the reflectingplate, the front end of the second barrel being provided with anopening, a lens in said tube in the path of light rays reflected fromthe mirror for directing them in substantially parallel relation againstthe rear face of the reflecting plate, a translucent reference discmounted in the instrument between the lens and said front end opening inthe second barrel at about the focal point of the lens, whereby thereflection of said disc on the reflecting plate will appear to surroundthe smoke seen through the reflecting plate, said disc being dividedinto areas of different light densities for visual comparison with thesmoke, and means for keeping the central area of the disc from beingseen on the reflecting plate.

' ,6. An optical instrument for the observation of smoke issuing from astack, comprising a sighting barrel having an opening for light at itsfront end and an ocular opening at its rear end to permit said smoke tobe seen through the barrel, a rearwardly reflecting plate through only acentral area of which the smoke can be seen by an observer at saidocular opening, said plate being mounted in the barrel at approximately45 to its axis, the side of the barrel opposite to the rear face of saidplate being provided with an opening, a second barrel substantiallyparallel to the sighting barrel and provided in its side with an openingopposite to the side opening in the sighting barrel, a short tuberigidly connecting said side openings, a reflecting member in the secondbarrel at the end of said tube and having a reflecting surface parallelto the reflecting plate, the front end of the second barrel beingprovided with an opening for light, a lens in said tube in the path oflight rays reflected from said reflecting member for directing them insubstantially parallel relation against the rear face of the reflectingplate, and a translucent reference disc mounted in the instrumentbetween the lens and said front end opening in the second barrel atabout the focal point of the lens, said disc on the reflecting platearound said central area will appear to surround the smoke seen throughthe reflecting plate, said disc being divided into areas of differentlight 2 plate being mounted in the barrel at approximately 45 to theline of sight between said openings, a reflecting member positioned toreflect against the rear face of said plate light rays from only thevicinity of said smoke while it is being observed through the barrel bysaid observer, a lens mounted between said reflecting member and platein a position to direct said rays in substantially parallel relationagainst the plate, and a translucent reference disc mounted in theinstrument at about the focal point of the lens, said disc on thereflecting plate around said central area will appear to surround thesmoke seen through the reflecting plate, said disc being divided intoareas of different light densities for visual comparison with the smoke.

References Cited in the file of this patent UNITED STATES PATENTS683,203 Grubb Sept. 24, 1901 1,385,940 Ellicott July 26, 1921 2,154,374Byram Apr. 11, 1939 2,243,383 Leber May 27, 1941 2,336,239 French Dec.7, 1943 FOREIGN PATENTS 21,086 Great Britain of 1911 225,690 GreatBritain Dec. 11, 1924 350,236 Germany Mar. 16, 1922 OTHER REFERENCESIllumination Engineering Society Transcripts (London), vol. 3, 1938,Visual Telephotometry by Collier, pages 141-154.

